The composite structures are widely utilized because of their high mechanical resistance together with a very low mass. These structures are therefore widely used by the aeronautics industry for equipping the aircraft's external wall such as the radome located at the front of the aircraft and the aircraft fairing. However, these structures which are electrically insulating do not make it possible to establish an evacuation of the electrical currents during lightning strikes on the external wall, locally generating an area of high-density charges that can, on the one hand, damage the aircraft's external wall and, on the other hand, perturb the electrical installations contained under this external wall. The case of the radome is even more critical since, by definition, it cannot integrate the standard lightning current discharge devices, such as a metal grid inserted in the structure's surface that, because of the requirements for transparency with regard to radar waves, are not allowed.
It is known to equip the external wall of aircraft with conducting elements extending along the wall to attach the lightning and allow the discharging of the currents due to lightning strikes on the external wall of the radome towards an aircraft ground, which is generally the fuselage.
FIGS. 1A and 1B show such a conducting element presented in the form of an electrically conductive strip 1 typically in aluminum or copper installed on the external surface 9 of the radome 3 of an airplane. The radome's main function is to protect a radar, consequently it is made of an electrically insulating composite material permeable to electromagnetic waves. The strip is fitted on the radome by fastener means 8 such as a screw. Each lightning conductor strip 1 is electrically linked to the external surface 9 of the radome 3 to allow the electrostatic charges that build up there to be discharged. The part 5 in which the screw is fitted to fasten the strip 1 is in insulating plastic.
This strip is electrically connected to the junction of the airplane's fuselage to ensure that it is grounded individually. Thus the conductive strip makes it possible to attach the lightning and establish the discharging of the currents due to lightning strikes on the external wall of the radome towards the ground without affecting any other element of the radome.
Such an anti-lightning system generally gives good results for external walls that do not have requirements in terms of aerodynamics. Nevertheless, it has been observed that the unevenness between the external surface 9 of the radome 3 and the conductive strip 1 that forms a step 20 are sources of discontinuity in the airflow 23 over the external surface of the aircraft, and as a result of turbulences 4 that lead to a reduction in the aircraft's aerodynamic performance (FIG. 1b).
However the generally conically-shaped radome located on the aircraft nose constitutes a main contribution to the aircraft's aerodynamics, thus it is essential to avoid these perturbations in order that the aircraft's aerodynamic performance is not penalized.
In effect, the consequence of these aerodynamic perturbations is to generate drag, increased by the triggering of the laminar/turbulent transition, and consequently a very noticeable rise in the airplane's consumption of fuel, which is incompatible with the economic requirements of the airlines.
It would therefore be beneficial to have a system protecting an airplane's radome against lightning allowing drag to be reduced so as to produce a significant saving in fuel weight.